The present invention relates generally to vehicle suspension systems and more particularly to vehicle suspension systems of the trailing arm type in which the arms are supported by the cooperative effort of primary and secondary springs.
Air springs, as often used in suspension systems for commercial vehicles, cnsist essentially of an air inflated bag interposed between the frame and an associated axle carrying member. While air springs are highly desirable particularly in passenger type commercial vehicles due to their ability to provide a smooth ride, they have relatively no lateral stability. Accordingly, such suspension systems have included a wide variety of torque rods, lateral stabilizer bars, bolsters, and other assorted and often times complex control systems. Often these lateral stabilizing arrangements require the use of substantial hardware members below the frame of the vehicle which requires raising the height of the frame so as to assure sufficient room for movement of the hardware members as well as assuring sufficient vehicle ground clearance. Additionally, these complex suspensions result in increased costs both in terms of manufacture and maintenance as well as creating the potential of increased out-of-service time for the vehicle.
There has recently been an increased concern with regard to designing public facilities to accommodate use thereof by the physically handicapped. Such design considerations have been seen through the use of ramps versus steps at building entrances, cut down curbs at cross walks and are now becoming increasingly important in the design of passenger-type commercial vehicles, such as buses or the like. Both ramps and lift platforms have been used in adapting such vehicles so as to enable boarding by the physically handicapped and in particular those individuals who are confined to wheel chairs. While lift platforms are able to accommodate relative large vehicle heights, they are rather complex requiring both substantial space as well as additional equipment. Ramps, however, offer the advantage of simplicity, reduced weight and space economy. However, in order to accommodate the use of a reasonable length ramp without providing an impossibly steep slope, it is necessary to reduce the height of the vehicle floor level to an absolute minimum.
Accordingly, the present invention provides an improved vehicle suspension system which overcomes the above disadvantages of prior suspension systems in providing a relatively uncomplicated suspension system which enables the vehicle floor height to be substantially reduced without sacrificing ride performance or excessively reducing ground clearance. The suspension system of the present invention is designed to be used in conjunction with driving, non-driving and/or steering wheels and comprises a pair of trailing arms pivotably secured to the frame assembly each of which has an air spring operatively associated therewith. A transversely extending leaf spring is also provided extending between the trailing arms and connected thereto with a center portion secured directly to the frame assembly. Both the leaf spring and air springs cooperate to support the vehicle weight with the leaf spring also operating to impart lateral stability to the suspension system. Preferably, both the leaf spring and air springs will each be selected to support their full share of the vehicle weight without assistance from the other spring means thereby enabling the vehicle to be operated in the event one or the other of the spring means is disabled. Also, the use of a transverse leaf spring does not interfere with or reduce ground clearance of the vehicle because it is attached to inner sidewall surfaces of the trailing arms. Thus, the floor height of the vehicle may be reduced to an absolute minimum so as to facilitate adaptation of the vehicle for use by the physically handicapped.
Additional advantages and features of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the claims and drawings appended hereto.